HK1129262B - Electronic method for starting a compressor - Google Patents

Description

Electronic method for starting a compressor

Technical Field

The present invention relates generally to a method and apparatus for starting a capacitor start capacitor run motor, and more particularly to starting a reversible CSCR motor for driving a compressor.

Background

Electric motors are commonly used to drive the shaft of compressors used in heating, ventilation and air conditioning (HVAC) systems. The motor may be an Alternating Current (AC) Capacitor Start Capacitor Run (CSCR) motor. CSCR motors can conveniently run on single phase AC power, such as between standard 230V AC commercial or residential power system lines. CSCR AC motors have two coils, a "run" coil and a "start" coil. Motion is created in the rotor of the motor by causing a phase difference between the AC currents in the two coils. This phase difference is caused by introducing a capacitor in series with one of the coils.

The CSCR motor is started by momentarily introducing a large capacitance to provide a high mechanical starting torque. Once the rotor speed is started to the desired speed, the starting capacitance is typically switched out of the circuit by a relay, leaving a smaller value of the run capacitor in the circuit to establish the correct phase relationship between the start and run coils for continued operation. Typically, the voltage across one of the coils (usually the start coil) is monitored using a voltage relay to determine when to open the start capacitor relay. If the start capacitor relay is opened prematurely before the motor achieves a sustained shaft rotational speed, the motor will stall when the start capacitor relay is opened. If the starting capacitor relay is opened too late, the coil current and voltage may become too high, potentially resulting in high temperatures, damaging mechanical stresses, and insulation breakdown. The accuracy of the voltage relay is only about 20 VAC, which limits the ability to accurately time the opening of the starting capacitor contactor. What is needed is a system that more accurately matches the opening of the motor start relay to the desired mechanical rotor condition. The mechanical rotor condition is also affected by line voltage, ambient temperature, motor temperature, and compressor conditions (such as how recently the compressor has been operating). Therefore, there is also a need for a system to vary the operation of the motor starting capacitor relay to compensate for factors such as line voltage, ambient temperature, motor temperature, or compressor operating conditions.

Another desirable feature of CSCR motors is that they can operate as reversible motors, where the shaft can be powered to rotate clockwise or counterclockwise. The direction of rotation can be forced by setting the phase of the current in the run winding to lead or lag the phase of the current in the start winding. This can be achieved by placing a capacitor in series with one or the other coil and connecting the remaining coils (typically two wires of a three-phase power supply) directly across the supply voltage. This switching can be accomplished by using two sets of contacts, usually in the form of contactors, one for forward rotation and one for reverse motor shaft rotation.

Two directions of rotation are particularly desirable for driving the compressor shaft of modern compressors. Such compressors can utilize a compressor shaft technology in which the compressor produces two different compression ratios as the shaft rotates in different directions. The principle of operation is that when rotating in one direction, the mechanical mechanism operates fewer pistons than when rotating in the opposite direction. Typically, a forward rotation operates two pistons, while a reverse rotation results in one piston operating. The problem is that the preferred conditions for opening the starter relay differ for both directions due to different mechanical loads. Therefore, there is also a need for a system to vary the operation of a capacitor start relay as a function of the desired direction of rotation.

Another issue in CSCR motor operation is the reliability of the motor starting capacitor relay. Even if the motor starting capacitor relay operates at the correct time for the correct mechanical shaft condition, the arc caused by opening the motor starting capacitor relay may reduce the life of the relay, or even cause a contact fault that may damage the capacitor or motor, by which time the starting capacitor cannot be removed from the circuit after an otherwise successful motor start. Therefore, there is also a need for a system to open the motor starting capacitor relay to result in a minimum electrical stress on the electrical contacts of the relay.

Disclosure of Invention

The motor starting apparatus includes a motor start relay for switching a motor start capacitor to a motor circuit across the run capacitor. The motor start capacitor increases an Alternating Current (AC) current flowing through a motor coil to start the motor. The motor starting apparatus also includes a system control to control a motor start relay and at least one contactor to apply power to the motor starting apparatus. The system control includes an electronic voltage measurement circuit to measure the coil voltage of the motor coil. The system control also includes a microprocessor to run an algorithm that causes the system control to switch the starting capacitor out of the motor circuit when the measured winding voltage exceeds a winding voltage threshold.

The method of starting a motor includes the steps of: providing a motor to be started, the motor having a motor start coil; providing a motor starting apparatus comprising a system control, a motor starting capacitor and a motor starting capacitor relay to switch the motor starting capacitor to a motor circuit and a coil voltage electronic measurement circuit; providing a contactor to supply electrical power to start and run the motor; signaling motor start to the system control; determining a motor coil voltage threshold; closing the motor starting capacitor relay when needed; closing a contactor to supply power to the motor starting apparatus and the motor circuit; measuring the coil voltage; comparing the measured coil voltage to a threshold voltage; and the starting capacitor relay is opened when the measured coil voltage exceeds a voltage threshold indicating that the motor has started.

Description of the drawings:

for a further understanding of these and objects of the invention, reference is made to the following detailed description of the invention, taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates one embodiment of a motor starting apparatus in accordance with the present invention;

FIG. 2 shows a simplified block diagram of the steps of an exemplary motor start sequence;

FIG. 3 illustrates an exemplary time line for operation of the motor starting apparatus;

FIG. 4A is one of exemplary algorithm fragments that can be run on the system control; and

fig. 4B is a second example algorithm fragment that can run on the system control.

Detailed Description

One embodiment of a motor starting apparatus according to the present invention is shown in fig. 1. The method and apparatus of the present invention for starting an electric Capacitor Start Capacitor Run (CSCR) motor 101 involves the operation of a start capacitor relay 112. The function of the start capacitor relay 112 is to engage the start capacitor 110. We describe herein methods and embodiments of a corresponding motor starting apparatus that can more preferably operate starting capacitor relay 112 for two more efficient CSCR motor starts and can reduce the likelihood of failure of CSCR motor 101, motor starting capacitor 110, starting capacitor relay 112, and other related electrical, electronic, and mechanical components.

Various embodiments of the present invention address the problem of inefficient CSCR motor starting by more precisely controlling the operation of the starting capacitor relay 112 based on measurements and factors including (independently or in any combination thereof): accurate measurement of CSCR motor coil voltage (potential); consideration of the required motor direction; including timing control during a CSCR motor start sequence elapsed from contactor closure; measured line voltage, measured outdoor temperature. Returning to fig. 1, we first describe the components of an exemplary CSCR motor control apparatus that can be used to implement various embodiments of the method of the present invention. CSCR motor 101 rotates a mechanical shaft (not shown) of compressor 104 (not shown in detail). CSCR motor 101 includes a start winding 103 and a run winding 102. A hot plug 105(thermal shutdown) senses the motor 101 temperature and opens the circuit to both motor coils in the event of an overheat condition. CSCR motor 101 can be supplied by line voltage 117 to a potential between two lines of a typically multi-phase power supply, such as two phases of a three-phase power supply.

The phase difference between the currents in the run and start coils causes the CSCR motor 101 rotor shaft to move. This phase difference is maintained by a run capacitor 111, which capacitor 111 is always in series with the run or start coil, as selected by the closing of contactor 108 or contactor 109. The direction in which the rotor shaft (not shown) of CSCR motor 101 rotates is established by closing contactor 108(HI) or contactor 109 (LO). System control 116 monitors the voltage V across the run coil_R113 and a voltage V across the starting coil of the motor 101_s114. By monitoring one or the other or both of these potentials with respect to time, the system controls, if any, as described further belowThe control 116 can advantageously determine how long the starting capacitor 110 needs to be in the circuit for an optimal motor 110 starting event. Note that compressor 104 mechanically begins with compressor piston motion caused by the onset of CSCR motor 101 rotor motion. Note also that for any given starting direction, the "start coil" places run and start capacitors in series with one coil or the other, depending on whether contactor 108 or contactor 109 is energized. For example, when contactor 108 is closed, line voltage is supplied directly to coil 102, labeled "run", and through run capacitor 111 to coil 103, labeled "start" in fig. 1. However, for a reverse motor rotor direction, if contactor 109 is closed, line voltage is supplied directly to coil 103 and phase-shifted to coil 102 through capacitor 111.

Because of the electrical, electromechanical, and magnetic forces associated with each motor start, optimal motor start events are important. Less than ideal starting, caused by having the motor starting capacitor remain in the circuit for too long, can cause damage to the starting capacitor, the motor and the compressor. Catastrophic failure of these components may result from accumulated damage such as long term poor motor start timing (leaving the start capacitor in the circuit too long or not long enough). A single extremely poor timed start may also lead to catastrophic damage.

Some prior art CSCR motor starting systems rely on a fixed delay time for engaging the motor starting capacitor ("timed start"). Other prior art CSCR motor starting systems utilize electromechanical voltage relays, typically voltage relays placed across the start coil or run coil. The relay removes the start capacitor from the start coil circuit when the coil voltage reaches a predetermined potential set on the voltage relay.

Although slightly better than pure timed starting, voltage relay based starting systems are far from optimal. To create a near-optimal start, the voltage across the motor coils needs to be determined more accurately than using a voltage relay. Typical relays used in motor starting applications typically have an accuracy on the order of 10%, and the threshold setting is also a function of the voltage relay coil resistance as a function of the coil temperature. Variations in coil resistance caused by variations in coil temperature can result in an additional 10% potential error, which results in a total 20% tolerance. Other factors than the accuracy of the motor coil voltage that can advantageously result in better motor starting are the motor line voltage, the compressor ambient temperature.

Returning to fig. 1, CSCR motor start-up may be improved by using electronic voltage measurement techniques with temperature compensation including voltage comparators or analog-to-digital converters (ADCs), generally represented by system controller 116 and motor coil voltages 113 and 114, according to one embodiment of the present invention. These coil voltage measurements can be accurate to about 1% or better than the 10% to 20% accuracy available in prior art motor starting systems using electromechanical voltage relays. Additional details of an exemplary electronic circuit that is well suited for making accurate voltage measurements in the motor starting System Control 116 are further described in co-pending U.S. patent application Ser. No. __/__, ___, entitled "Integrated Measurement of AC Voltage Using the Control Microprocessor of an HVAC System", filed 2006, ____, ____, which is incorporated herein by reference in its entirety.

An exemplary motor start sequence using the motor coil voltage measurement described above is illustrated by the block diagram of FIG. 2, and the process is as follows: (a) the motor start capacitor relay 112 may be activated by the system control 116, causing the contacts 115 to close, thereby inserting the motor start capacitor 110 into the motor circuit, (b) after a brief delay, the system control 116 can power the contactor 108 or 109 to send power to the CSCR compressor motor, starting the compressor in one direction or the other (clockwise or counterclockwise shaft rotation), and (c) when the compressor shaft reaches a predetermined speed as indicated by a predetermined motor coil voltage measurement, the system control 116 may de-power the motor start capacitor relay 112, which causes the contacts 115 to open, thereby removing the motor start capacitor from the motor circuit. The system control 116 adds a delay before de-energizing the starter relay 112 that causes the contacts 115 to open, thus ensuring that the current flowing through the contacts 115 is extremely low when open. When the start fails, the system control de-energizes the contactor 108 or 109, removing system power for a short period of time before opening the starter relay contacts 115. With this sequence, contacts 115 of motor start capacitor relay 112 are advantageously never exposed to high start currents because power is not applied to the motor circuit until contactor 108 or 109 is closed, start capacitor 110 power is removed when the capacitor current is very low when a successful start, and contactor 108 or 109 removes system power before de-energizing start relay 112 when a compressor start fails. Thus, the contacts 115 are not prone to pitting (pitting) or solder failure. Also note that in this embodiment, exemplary motor start capacitor relay 112 is a relay having "normally open" contacts, and power needs to be supplied to the coil of motor start capacitor relay 112 to close the contacts. Thus, in the unlikely failure of the motor starting capacitor relay 112 coil, the contacts 115 are opened and the motor starting capacitor 110 is removed from the motor circuit.

According to another embodiment of the present invention, the desired CSCR rotor direction may be considered when determining that the operating motor starting capacitor relay 112 is removing the motor coil voltage of motor starting capacitor 112 from the circuit. The decision to determine the threshold voltage by rotor direction is important because certain compressors, such as the twin single ("TS") compressor manufactured by Bristol compressor, have two modes of operation. Using the patented cam mechanism, the TS compressor operates one piston when the compressor shaft rotates in one direction and two pistons when the shaft rotates in the opposite rotational direction. Thus, the compressor is a two-stage compressor, wherein a clockwise compressor rotor direction results in a first compressor capacity stage and a counterclockwise compressor rotor direction results in a second compressor capacity stage. When the rotor of the electric motor 101 is mechanically coupled to the shaft of the TS type compressor 104, the mechanical torque required to rotate the compressor, and in particular the compressor shaft, past top dead center ("TDC") is different for one piston operation and two cylinder operation. In other words, there are two different mechanical load conditions for either clockwise or counterclockwise compressor rotor operation. Thus in the TS configuration, for a better CSCR motor start, two different starting voltage thresholds need to be used due to different loads in the direction of rotation. The solution is to use separate starting voltage thresholds for starting the reversible motor compressor in either direction of rotation. The starting voltage threshold is stored in the microprocessor memory to be read and used at start-up.

According to the exemplary CSCR motor starting apparatus of fig. 1, the system control 116 can command a particular rotor direction (i.e., clockwise or counterclockwise) by energizing either contactor 108 or contactor 109. An algorithm running on a microprocessor on system control 116 commands direction and/or accesses the commanded rotor direction and can select an appropriate voltage threshold to open contacts 115 of motor capacitor start relay 112 based on the commanded rotor direction. Note that only one motor capacitor start relay 112 is required regardless of the commanded direction to start the contactor 108 or 109. An exemplary motor start sequence that is sensitive to the commanded motor rotor direction is the same as described above, except that in step (c), the predetermined motor rotor speed threshold indicated by the voltage threshold is different for the commanded clockwise rotation and the commanded counterclockwise rotation.

Yet another embodiment of CSCR motor starting apparatus 10 can utilize timing delays to further protect CSCR motor 100, motor capacitor start relay 112, motor start capacitor 110, and other motor starting apparatus 10 components. Damage to motor capacitor start relay 112 may occur if the relay closes contacts 115 with a sufficiently high residual voltage stored in start capacitor 110. In this case, a high current can be immediately driven through the relay contacts 115, welding them closed. Furthermore, breaking the contacts 115 when a large amount of current flows through the contacts 115 can damage the contacts by transferring contact material from one contact to another, as well as possibly soldering the contacts. High starting circuit voltages may also be present if the contactor is closed before the relay is powered (normal operation) or opened after the relay is de-powered (failure of the start mode). However, as shown in the exemplary timeline diagram in fig. 3 (and comparing the exemplary timelines of the motor starting apparatus shown in fig. 1), motor capacitor start relay 112 contact 115 can be closed for at least one second before contactor 108 or 109 is energized. Under normal operation, the relay contacts 115 will not supply voltage to the starting circuit, and when a start failure occurs, the relay contacts 115 will not apply a breakdown voltage to the starting circuit, thus avoiding damage to the contacts 115 due to high starting current. Note that in the exemplary timeline of FIG. 3, "μ PC" represents a microprocessor running a control algorithm on the system control 116. The compressor represents a compressor 104 driven by a motor 101 and depending on the motor shaft direction (clockwise or counterclockwise, as desired), the contactor is either a contactor 108 or a contactor 109.

The bleeder resistor (not shown) is a power resistor of extremely robust design. A relatively high resistance value bleed resistor may be typically connected across the terminals of motor start capacitor 110. The function of the bleeder resistor is to dissipate any remaining energy stored in the motor starting capacitor 110 after the motor capacitor starting relay 112 contacts 115 open, removing the capacitor from the motor circuit. Failure of the bleed resistor may result in incomplete "bleed" or discharge of the capacitor voltage, causing the relay contacts to weld on the next start. Welded contact on the next start will also tend to cause motor starting capacitor 110 to fail because motor starting capacitor 110 will be held in circuit for a few seconds until the compressor motor overload trips.

If there is a fault in the motor starting apparatus 10, for example, if the bleeder resistor on the motor start capacitor 110 fails to open, there may not be enough time for the stored capacitor voltage to decay inherently to a safe level before the next start after the motor capacitor start relay 112 contacts 115 open. The problem is that subsequent start attempts will likely result in the contacts 115 being welded together as described above. To avoid this possibility, a time delay is incorporated that will not allow for successive starting attempts until the motor start capacitor 110 has sufficiently leaked after a failed or successful start. Even without the bleed resistor, motor start capacitor 110 can inherently discharge by itself, although this takes a longer period of time than the bleed resistor helps. Thus, to allow discharge through intrinsic discharge in the event of a leaky resistor failure, the minimum system run time after a successful start may be set to a minimum of 3 minutes, and the minimum time between start attempts may be set to 5 minutes.

A related problem is that the starting capacitor will fail if left in the circuit too long. At the voltage and current levels produced by a motor with engaged starting gears, the allowable capacitor duty cycle is approximately 1 second on time and 59 seconds off time. The off time is needed to prevent damage from high capacitor currents and to allow any internal heat generated during the ON period to dissipate. The solution to this problem is to power only the motor capacitor start relay 112 for 1 second or less after the contactor 108 or 109 is powered to apply the circuit voltage. If the compressor is not activated at this time, consider "no activation" and the contactor 108 or 109 may be de-energized to remove the circuit voltage. The starter relay can then be de-energized for 1 second to allow the starter capacitor voltage to leak through the compressor coil to a safe level in this case and to minimize current flow for relay contact breakdown. The coil provides a small resistance to thereby leak current, and thus, leaks at a faster rate than through a leakage resistor. Moreover, there is no large current between motor start capacitor 110 and run capacitor 111 because they are always at the same voltage level during leakage. If the compressor fails to start, the system control 116 can be preprogrammed to wait 5 minutes to try again. If there are 3 consecutive "no starts," there may be another 30 minute delay before the next compressor start attempt. These two delays can help protect motor start capacitor 110 by maintaining operation within its rated duty cycle. Thus, the algorithm can limit the time that voltage is applied to the starting capacitor so that the starting capacitor duty cycle limit is not exceeded.

Example (c):

fig. 4A and 4B show a flow chart of an algorithm that can run on a microprocessor on the system control in the preferred embodiment using voltage thresholds and time delays as described above (one flow chart spans both graphs). The sequence of steps begins with "start up". A counter that may be used to monitor the number of consecutive start attempts is initialized to "0". The motor capacitor start relay is energized and then after 1 second, the motor start contactor applies electrical power to the motor start circuit. The system control monitors the motor coils by making voltage measurements. The voltage measurement is compared to a coil voltage threshold. As indicated by reaching the threshold voltage, if the voltage measurement indicates that the motor is up to the threshold rotor speed, the start relay is de-energized and the compressor is running normally after a "good" start. On the other hand, if the voltage measurement is below the threshold voltage, the algorithm loops, taking successive voltage measurements and comparing each measurement to the threshold voltage until the threshold is reached or the timer reaches 1 second and "times out", causing the start counter to increment by 1 and the timer to reset. Then, the contactor was de-energized, a time delay of 1 second occurred, and then the motor start relay was de-energized. The counter is then checked to see how many start attempts have occurred. If less than 3 start attempts occur, after a 5 minute delay, another start attempt is initiated. If 3 unsuccessful start attempts occur in succession, a delay of 30 minutes is introduced before attempting the next start attempt. Note that if the compressor started successfully on the fourth attempt after a 30 minute delay, both the timer and the counter are reset to 0. By using such a relatively long time delay, transient fault conditions can be automatically tolerated without otherwise causing the electromechanical fault protection device to fail in a manner that may require intervention by a repair technician to restart the faulty system and a corresponding long downtime of the home or office comfort system.

In yet another embodiment, instead of relying on only one starting voltage threshold, or two starting voltage thresholds (one for each rotor direction), the voltage threshold may be calculated based on one or more measurements. For example, during start-up, the start coil voltage generated by the compressor can be shown to increase or decrease as the line voltage increases or decreases. The system control can continuously or periodically measure the line voltage used to power the motor starting apparatus, and then one or more starting voltage thresholds can be adjusted to compensate for the high or low line voltage. In fact, for certain high line voltage conditions, a motor start capacitor may not be required for a given motor and compressor. This information can be used by programs running on the system control.

In yet another embodiment, the system control may have a measurement input of the outdoor temperature. The combination of outdoor temperature and compressor "off time may be important factors for determining the optimal voltage threshold. For example, after a long shut-down time, the refrigeration circuit compensates for the suction to relieve the pressure differential, thus reducing the starting torque requirement to a point where no starting capacitor assistance is needed. Limiting the number of times the motor starting capacitor is actually used can improve the life of the motor starting capacitor and starting capacitor relay. Also, lower torque level starts improve compressor life because these starts can be done with low pressure to the coils, rotors, laminations, bearings and throw block.

In yet another embodiment of the present invention, the contactor is capable of operating only when the motor starting capacitor is engaged and the capacitor voltage and/or line voltage measurement is near zero volts. The compressor motor start can thus be further improved by operating the start capacitor relay only at the point of minimum potential of the AC sinusoid. The minimum potential is defined herein as a voltage of 10% or less of the peak AC voltage under consideration.

It should be noted that the system control 116 can run one or more algorithms as described above to implement the inventive methods of the various embodiments of the present invention. Typically, such algorithms run in software or hardware on a microprocessor. As used herein, the term microprocessor (or microcomputer) includes microcontrollers, which generally contain memory, input/output (I/O) functions in a microcontroller package; or a microprocessor with separate memory and separate I/O attached to the system control 116. Other suitable processors for running such algorithms include, but are not limited to, microprocessors, microcontrollers, or complex logic elements such as Field Programmable Gate Arrays (FPGAs), other types of gate arrays, or other types of programmable logic capable of performing processor-like functions to run programs that perform the functions described herein.

The term electronic measurement circuit denotes an electronic circuit comprising a voltage comparator and an analog-to-digital converter (ADC) of all suitable types, and also an electronic measurement circuit comprised in a microcontroller. The term electronic measurement circuit does not include prior art electromechanical voltage relays.

Motor capacitor start relay 112 has been described as an electromechanical relay with contacts 115. It should be noted that an electronic or electrical switching device with a suitable contact rating may be used instead of a relay. For example, other types of contactors or solenoid operated contacts could be used instead of conventional relays.

While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.

Claims (20)

1. A motor starting apparatus comprising:

a motor start relay for switching a motor start capacitor into a motor circuit across the run capacitor, the motor start capacitor increasing an Alternating Current (AC) current flowing through a motor coil to start the motor; and

a system control to control the motor start relay and at least one contactor to apply power to the motor starting apparatus, wherein the system control includes an electronic voltage measurement circuit to measure a coil voltage of the motor coil, the system control further including a microprocessor to run an algorithm such that the system control switches the start capacitor out of the motor circuit when the measured coil voltage exceeds a coil voltage threshold.

2. The motor starting apparatus of claim 1 further comprising at least two coil voltage thresholds, wherein a first coil voltage threshold is used for commanded clockwise motor rotor rotation and a second coil voltage threshold is used for counterclockwise motor rotor direction.

3. The motor starting apparatus of claim 2 wherein the motor starting apparatus is used to start a Capacitor Start Capacitor Run (CSCR) motor to rotate a compressor rotor on a two stage compressor, and wherein a clockwise compressor rotor direction results in a first compressor capacity stage and a counterclockwise compressor rotor direction results in a second compressor capacity stage.

4. The motor starting apparatus of claim 1 wherein the system control further measures a line voltage used to power the motor starting apparatus and the motor circuit, and the system control calculates the coil voltage threshold based at least in part on the measured line voltage.

5. The motor starting apparatus of claim 1 wherein the system control also measures an outdoor temperature, and the system control calculates the coil voltage threshold based at least in part on the measured outdoor temperature.

6. The motor starting apparatus of claim 1 wherein an algorithm running on the system control commands contactor closure to apply power to the motor circuit without switching the motor start capacitor into the motor circuit, wherein the algorithm determines that the motor start capacitor is not needed for a particular motor start event.

7. The motor starting apparatus of claim 6 wherein the decision not to switch into the motor starting capacitor is based on measurements selected from the group of measurements consisting of line voltage, rotor direction, compressor off time, and outdoor temperature.

8. The motor starting apparatus of claim 1 wherein the algorithm includes a counter to count the number of consecutive start attempts since the last successful motor start event, the algorithm adding a time delay between unsuccessful start attempts.

9. The motor starting apparatus of claim 8 wherein the time delay is at least 5 minutes for the first 3 unsuccessful start attempts and the time delay is at least 30 minutes after the third unsuccessful start attempt.

10. The motor starting apparatus of claim 1 wherein the algorithm running on the system control adds a time delay between powering the motor start relay and closing the contactor to apply power to the motor circuit or the algorithm running on the system control adds a time delay to limit the time voltage applied to the starting capacitor from exceeding a starting capacitor duty cycle limit.

11. The motor starting apparatus of claim 1 wherein the algorithm is such that the system control switches the starting capacitor out of the motor circuit when the measured winding voltage exceeds a winding voltage threshold and the voltage on the AC sinusoid of the line voltage is within 10% of a minimum voltage.

12. A method of starting an electric motor comprising the steps of:

providing a motor to be started, the motor having a motor circuit including a motor start coil;

providing a motor starting apparatus comprising a system control, a motor starting capacitor, and a motor starting capacitor relay for switching the motor starting capacitor to the motor circuit and to a coil voltage electronic measurement circuit;

providing a contactor to supply electrical power to start and run the motor;

signaling motor start to the system control;

determining a motor coil voltage threshold;

closing the motor starting capacitor relay when needed;

closing a contactor to supply power to the motor starting device and motor circuit;

measuring a coil voltage using the coil voltage electronic measurement circuit;

comparing the measured coil voltage to a voltage threshold; and

the starting capacitor relay is opened when the measured coil voltage exceeds a voltage threshold indicating that the motor has started.

13. The method of claim 12 wherein the step of determining a motor coil voltage threshold comprises the step of determining a motor coil voltage threshold based on a commanded motor rotor clockwise or counterclockwise direction.

14. The method of claim 13 wherein the step of providing a motor requiring startup comprises the step of providing a Capacitor Start Capacitor Run (CSCR) motor requiring startup to rotate a compressor rotor on a two stage compressor and wherein a clockwise compressor rotor direction results in a first compressor capacity level and a counterclockwise compressor rotor direction results in a second compressor capacity level, the motor having a motor start coil.

15. The method of claim 12, wherein the step of determining a motor coil voltage threshold comprises the step of determining a motor coil voltage threshold, wherein the system control also measures a line voltage of electrical power, and the coil voltage threshold is determined based at least in part on the measured line voltage.

16. The method of claim 12, wherein the step of determining a motor coil voltage threshold comprises the step of determining a motor coil voltage threshold, wherein the system control also measures an outdoor temperature, and the coil voltage threshold is determined based at least in part on the measured outdoor temperature.

17. The method of claim 12 wherein said step of closing said motor start capacitor relay when needed comprises the step of closing said motor start capacitor relay when needed, wherein said need is determined based on measurements selected from the group of measurements consisting of line voltage, rotor direction, compressor off time, and outdoor temperature.

18. The method of claim 12 further comprising the steps of counting the number of consecutive start attempts from the last successful motor start event and adding a time delay between unsuccessful start attempts.

19. The method of claim 18, wherein the step of adding a time delay comprises the step of adding a time delay between unsuccessful start attempts, wherein the time delay is at least 5 minutes for the first 3 unsuccessful start attempts and the time delay is at least 30 minutes after the third unsuccessful start attempt.

20. The method of claim 12, further comprising the step of adding a delay between the step of closing the motor starting capacitor relay and the step of closing a contactor to supply power to the motor starting device and motor circuit when needed, or adding a delay from opening of a contactor to remove power from the motor starting device and motor circuit where the motor has not reached the voltage threshold before the step of opening the starting capacitor relay.